The invention relates generally to inspection systems and more specifically to a method and system for automated eddy current nondestructive testing.
Eddy current inspection is a commonly used technique for nondestructive inspection of aircraft engine and other industrial components for surface flaws. The technique is based on the principle of electromagnetic induction, wherein a drive coil carrying alternating currents induces eddy currents into a part under test. In the case of a flaw in the test specimen, as for example, a crack or a discontinuity, the eddy current flow within the test specimen alters, which can be detected by one or more sense coils. The detected signals are used to generate an eddy current image, which can be analyzed further to detect the presence of flaws in image.
Attempts have been made to develop automatic flaw detection processes for eddy current images. U.S. Pat. No. 5,345,514, Mahdavieh et al., entitled “Method for inspecting components having complex geometric shapes,” discloses one such technique, which uses references images from adjacent structurally similar portions to perform the processing. Typically, a surface of a component is scanned with an eddy current probe and a two-dimensional image of the scanned portion is generated using the eddy current signals received during scanning. The image is preprocessed to reduce any signals relative to the background pixel intensities in the image caused by geometric characteristics and background noise common to all similarly shaped structural portions. Any suspected defect regions are identified from the preprocessed image, and a defect characterizing parameter is determined for each suspected defect region. Typically, if any defect characterizing parameter exceeds a predetermined reference value, the suspected defect region is rejected.
The above described method may have certain disadvantages, including a lower probability of detection, due to less effective encapsulation of the flaw patterns seen in the eddy current images acquired by the system. Another disadvantage of the above described process, is the fact that two reference images obtained from adjacent structural portions of the component under inspection are required as inputs to the process, for suppressing strong edge signals which mask the underlying crack signals. Availability of such reference images may be difficult for real-time inspections.
Thus, there is a need to develop a more precise method of eddy current inspection that would automatically detect defects in real time and characterize the size of the defect.